Ultrahigh-frequency heater



P. W. MORSE ETAL ULTRAHIGH-FREQUENCY HEATER Filed Sept. 15, 1948 Jan. 22, 1952 er Inventors: philip W. Morse, Maurice T`. Davis,

by Thenr` Attorney.

Patented Jan. 22, 1952 ULTRAHIGH-FREQUENCY HEATER Philip W. Morse, Elnora, and Maurice F. Davis,

' Syracuse, N. Y., assignors to General Electric Company, a. corporation of New York Application September 15, 1948, Serial No. 49,444

s claims. 1

Our invention relates to ultra highv frequency heaters and more particularly to ultra high frequency heaters of the type employing a heating chamber having walls made of electrically conducting material and in which standing electro magnetic Waves are produced for the heating of a material in the chamber. It is an object of our invention to provide simple and reliable means for mounting rollers extending through a high frequency heating chamber without changing substantially the standing wave distribution in the chamber `and without loss of energy from the chamber.

In carrying out our invention in one form we provide a heating chamber in the form of a resonant cavity having dimensions which will accomodate the material to be heated and at the Sametime provide suitable electromagnetic wave distribution at the frequency being used properly to heat the material. rollers extending across the chamber in parallel spaced relation and which carry the material to be heated have surrounding sleeves or chokes attached to the walls of the cavity and constructed to prevent the loss of high frequency heating energy.

For a more complete understanding of our invention, reference should be had to the accompanying drawing, Fig. 1 of which is a sectional view longitudinally through the heating chamber; and Fig. 2 is a top view, partially in section, of the heating chamber.

Referring to the drawing, we have shown our invention as applied to a rectangular heating chamber or cavity l having transverse and lengthwise dimensions correlated with respect to a high frequency supply source so that an electromagnetic field of suitable mode is established in the chamber. The heating chamber is made of suitable electrically conductive material and power is supplied to it from a high frequency supply source 2 through a transmission line 3 preferably of the concentric conductor type. The line 3 has its inner conductor extending inte` heating chamber l to form a radiating probe or loop at a suitable point positioned with respect to the frequency being used and the dimensions of the chamber to establish an electromagneticl field of the desired mode in the chamber. At the ends of the heating chamber or cavity are doors 4 and 5 and these are also of suitable electrically conductive material, preferably the same as4 the remainder of the heatingchamber. Door 4 is raised and lowered by vertical lifting means 4 while door 5 is pivoted about supports 5.

A plurality of dielectric Both doors are closed during lthe heating cycle to form a part ofthe heating chamber or cavity.

The material 6 to be heated passes through the heating chamber on rollers 1 made of lowloss dielectric material'whose structural characteristics are such that they support the material as it passes through the heating chamber. In order to provide a bearing foundation between the rollers and the walls of the heating chamber, without greatly distortingv the electromagnetic fields set up within the chamber andwithout loss of high frequency energy, the rollers pass through apertures 1 in the side walls of the chamber and then through cylindrical sleeves 8 concentrically surrounding the ends of the rollers. The sleeves 8 are made of a suitable electrically conducting material, preferably tlielsarne as the heating chamber itself and have their inner ends securely fastened to the side walls oi the heating chamber. l

The diameter of each vof the cylindrical sleeves 8 is such that the wave length'of the heating frequency energy is greater than the cut-off wavelength of the sleeve with the dielectric roller therein, or in other words, the frequency of the heating energy is less than the cut" off frequency. This means that the diameter oi" the sleeve is small enough to prevent passage o? the high frequency energy through the sleeve the usual wave propagation modes. In the case of a cylindrical sleeve of the type illustrated,

the radius of the sleeve must be smaller than the radius of a sleeve which would propagate the 'IEu mode of energy of the frequency of the heating energy. In all cases the presence of the di electric roller must be considered in the calculation of the diameter of the cylindrical sleeve in obtaining the proper cut-off wave length or frequency.

The length of each cylindrical or tubular sleeve 8 is such that sufficient attenuation is obtained along its length to prevent high frequency arcing in a ball bearing 9 located at the outer end ci each sleeve. The length of the sleeves can be any length greater than one quarter wave length which will give the desired attenuation. While it has been found that a sleeve length equal to approximately three quarters of a wave length generally provides suicient attenuation this length may be varied if necessary. By constructing the sleeves in the manner described to length and cross section, the loss of more than a negligible amount of high frequency energy through the sleeves is prevented. 'At the same time. the use of dielectric rollers prevents undue 3 distortion of the electromagnetic fields in the heating chamber.

The ball bearings 9 at the outer ends of the sleeves support the dielectric rollers l. @n end of each roller is mounted a sprocket it which is driven by a continuous chain il. The continuous chain may in turn be driven by a suitable means such as electric motor I2 through speed reduction gear- I3. The entire driving mechanism including chain and sprockets is external to the heating chamber and, therefore, has no eiect on electromagnetic .ields 4within the chamber.

Our invention makes feasiblerthe use of e roller conveyer system in an ultra high frequency heater because it both minimizes the distortion of the electromagnetic fields, in the heating' chamber due to the presence of rollers in the chamber and minimizes the loss of energy from the heating chamber due to the presence of the rollers` While we have illustrated and described our invention as applied to e furnace: designed for batch operation; it, can readily be adapted to continuous operation by substituting a suitable conveyor and suitable energy blockingopenings on the ends of the heating chamber such as, for example, the type disclosed in Patent No. 2,467,230-, issued on April l2, 19,49 to Henry Reveroomb and Donald E ll/dttsv and essisned to: the assignee oi this present invention.y

eeeordinelv.Y While We lieve described one preferred embodiment oi our invention by of illustration together with one modiicatior other modifications will occur` to thosey skilled the art and it should be. understood that We irl-- tend by the appended claims to cover all such modifications as `fall within the true spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

l. An ultra high frequency heater comprising a plurality of electrically conductive walls defining an elongated heating chamber provided with an opening at each end, means for supplyinshigh frequency energy to said chamber foi' producing standing electromagnetic waves therein, and means for passimif` a material to be heated through said chamber including a plurality of dielectric rollers extending in parallel spaced q relation with each other transversely across said chamber, the Walls of said chamber being provided with apertures through which said rollers project, tubular members of electrically conducting materiel surrounding the projecting ends of seid rollers,y in concentric leleition therewith, each of said members having its inner endsecured to a wall of said chamber and a bear-ingin the outer end of said tubular member for the end of its said roller. said tubular: members having e length greater than one quarter of the wave length of said energy and a diameter relative to said wave length to constitute s weve. snide having very high attenuation.

A2- All. oltre bien iredoenoy beater Comprising electrically conductive walls forming an elongated heating chamber provided with an opening at each end, av high rrequency supply source connected to said chamber for producing stand ,Die electromagnetic Waves in the chamber, means for passing a material to be heated through said chamber including a plurality of rollers mede oi dielectric materiel extending, in parallel spaced relation with each other transversely across tbe bottom of said chamber,y the vvalls` of said chamber being provided with apertures through which said rollers project, electrically conductive enclosing members surrounding each of the projecting ends of said rollers, the inner extremity o1" each of said members being securely fastened to the chamber wall, the outer extremity of said members containing a bearing supporting the end of its associated roller, each cisaid members having a length greater than one-quarter of the wave length of said source and transverse dimensions relative to said wave length to conn stitute a wave guide having very high attenua ation.

3. An u ltrav high frequency heater comprising an elongated heating chamber defined by electrically conductive vvalls of rectangular cross section with an opening at each end, electrically conductive closure members for said openings, means for supplying high frequency energy to said chamber, means for passing a material to be heated through saidv chamber including plurality of dielectric rollers extending in parallel spaced relation with each other transversely across the bottom of said chamber, the walls oi said chamber being provided with apertures through which said rollers project at each end. an electrically conductive tubular member surrounding each of said projecting ends of said rolle-rs in concentric relation therewith and ing its inner end secured to a wall of said chamber anda bearing in its outer end for the support of its said rollen said member having a length greater than one quarter of the wave length oi said energy and aI diameter relative to said wave length to constitute av wave guide having very high attenuation.

4. An ultra high frequency heater comprising electrically conductive walls forming an elongated heating chamber provided with an opening at each end, a high frequency supply source connected to said chamber for producing standing electromagnetic Waves in the chamber, means for passing a material to be heated through said chamber including a plurality rollers made of dielectric material extending in parallel spaced relation with each other transn versely across the bottom of said chamber, the walls of said chamber being provided with apertures through which said rollers project. electrically conductive enclosing members around the projecting ends of said rollers, the inner extremities of said members being securely iostened to the chamber wall,l the outer extrem @f Said members, QQllaIl-.ng Dealings supll i said rollers, each of saidlinembers having a length greater than onefcuarter the length of said source and transverse dimenr relative to said wave length to constitute a wa e guide having very high attenuation.

5. An ultra high frequency heater (confini-ismi:- electrically conductive walls forming an elem gated heating chamber provided with an opening at eeen. end. a high frequency supply s connected to said chamber for producing standing electromagnetic waves in the chamber. means Ifor supporting material to be heated and passing said material through said chai including a plurality of rollers made of diele material extending in parallel spaced rela on with each other transversely across the bottom of said chamber, the walls of said chamber provided with apertures through which sa,A ers project, electrically conductive enolosmg members around the projecting ends or said rollers, the inner extremities of said members being securely fastened to the chamber wall, the outer extremities of said members containing bearings supporting said rollers, each of said members having a. length greater than one quarter of the wave length of said source and transverse dimensions relative to said wave length to constitute a wave guide having very high attenuation.

PHUJIP W. MORSE. MAURICE F. DAVIS.

REFERENCES CITED The following references are oi' record in the file of this patent:

6 UNITED STATES PATENTS Number Name Date 2,364,526 Hansell Dec. 5, 1944 2,467,230 Rivercomb et al. Apr. 12, 1949 2,483,933 Rivercomb et a1. Oct. 4, 1949 2,500,752 Hanson et al Mar. 14, 1950 OTHER REFERENCES Skilling, "Physical Behavior of Wave Guides, Electronics, March 1943, pages '76-80, particularly pages 79 and 80.

Marcum et al., Heating with Microwaves, Electronics.. March 1947, pages 82-85, particularly page 83. 

